1. Field of the Invention
The present invention relates to a three-position actuator piston assembly, and an actuator system associated therewith, of the types utilized to control the double-acting clutches of a change-gear transmission, such as the splitter clutches or range clutches of a compound transmission. In particular, the present invention relates to a pressurized, fluid-actuated actuator piston assembly providing three selectable, maintainable positions (axially centered, axially displaced in a first direction, and axially displaced in a second direction) and requiring only a single controllable, variable pressure fluid supply device such as a pulse-width-modulated, solenoid-controlled valve. Preferably, the actuator assembly will provide selectably variable force in movements between the selectable axial positions thereof.
2. Description of the Prior Art
Change-gear mechanical transmissions having double-acting clutch mechanisms, of both the synchronized and non-synchronized types, are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,335,616; 4,428,469; 4,754,665; 4,920,815; 4,944,197; 5,086,897; 5,370,013 and 5,390,561, the disclosures of which are incorporated herein by reference. Two-position and three-position fluid-actuated actuator piston assemblies and actuator systems associated therewith also are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,899,607; 4,928,544; 4,936,156; 5,054,591; 5,193,410; 5,263,379; 5,272,441 and 5,329,826, the disclosures of which are incorporated herein by reference.
While the prior art fluid-actuated transmission shift actuators are widely utilized, for certain applications, they are subject to improvement, as they do not provide a selectable and maintainable intermediate (i.e., neutral or disengaged) position, they were of a complicated and/or expensive structure, they required two or more controlled sources of pressurized fluid and the associated control devices therefor and/or they did not provide selectably variable actuating forces in movements between the various selectable positions thereof.